In a conventional polymer electrolyte fuel cell (PEFC), fuel gas containing hydrogen and a gaseous oxidizing agent containing oxygen are respectively supplied to two gas diffusion electrodes (cathode and anode) sandwiching a polymer electrolytic membrane. The two gas diffusion electrodes and the polymer electrolytic membrane constitute a membrane electrode assembly (MEA). The gas diffusion electrodes are generally provided with a porous gas diffusion layer and a platinum catalytic layer. The gas diffusion layer is made from carbon and supports the catalytic layer. The platinum catalytic layer is connected to the electrolytic membrane. Gas which is supplied from the outside of the diffusion layer diffuses into the platinum catalytic layer through the diffusion layer. Reactions as shown in Equation (1) and Equation (2) occur at the electrodes and convert chemical energy into electrical energy.H2→2H++2e−  (1)1/2O2+2H++2e−→H2O  (2)
In a PEFC, water is generated at the cathode as shown by Equation (2). Since the fuel gas must be humidified in order to facilitate the above reactions, moisture is also supplied to the anode which performs the reactions as shown in Equation (1) above. As a result, water is always present at the gas diffusion electrode. When the fuel cell has not reached a normal operating temperature, it is sometimes the case that water in the gas diffusion electrode impedes the supply of gas to the platinum catalytic layer. Therefore it is preferred that water in the gas diffusion electrode is discharged rapidly. Furthermore when the ambient operating temperature of the fuel cell is low, water in the gas diffusion electrode freezes. Thus prompt melting and discharge of water in the gas diffusion layer electrode is preferred.
Tokkai 2000-223131 published by the Japanese Patent Office in 2000 and Tokkai Hei 8-138692 published by the Japanese Patent Office in 1996 disclose a fuel cell provided with a hydrophilic membrane on the surface forming a gas flow passage. In this fuel cell, discharge performance is improved with respect to water produced in the passage as a result of the hydrophilic characteristics.